I want to know to permanently fix back view mirrors. Last night, somebody stole them. Please tell me any solution.
Make your bike less accessible. Don't park it near where people walk past. Instead, park it down the row a little. Avoid parking it anywhere that will be in anyone's way—inconvenienced people may take it out on your bike.
Park your bike in a secure location if possible. That means not leaving it outside overnight; ideally bring it into a lockable garage or shed, or even into your home.
Make the accessory securely attached. That means no velcro, no quick releases, and no breakaway plastic. A downside: breakaway parts are a safety feature to reduce the chance of stabbing into you or someone else.
Also, look at the fasteners. If it's a thumbscrew like a GoPro, anyone can undo that without tools. So look for replacement metal bolts that can be torqued down tighter. Ideally the new metal bolts would be into metal fasteners—plastic ones may strip out easier.
To protect the bolt, you can use some weird security tool fitment that the thief won't be carrying on their person. Or consider putting a blocker in, like a ball bearing into a hex socket. You can retain it with candle wax or glue, annoying to remove legitimately.
Also prevent the bolt being removed by using a thread locker like locktite. Generic superglue/cyanoacrylate glue also works fairly well. Avoid the threadlockers that need heat to release, else you can't get your own parts off without a hot torch which will melt other things.
An additional thought—depending on how your bike bars are set up, it may be reasonable to wrap your bartape over the accessory fitments. This will obscure the fastener and make it take longer to interfere with your bike.
Naturally these suggestions won't make your bike theft-proof, just make it less-attractive and take longer to fiddle with.
There's no permanent fix, nor is there anything truly theftproof.
In my experience, if a thief tries to steal something which is not easy to steal, they will just break it in fustration. Which will make your life harder when it comes to removing the broken bracket.
I would just buy the cheapest one I could find, and maybe paint the back of it an ugly colour to deter someone wanting it. Replace the screw of bolt for a security torx and put some insulation tape around it to make it less obvious to the thief.
Same goes for lights and bells.
Also see this thread that discusses your problem more widely.
tldr; If you have something nice and want to keep it that way, take them with you.
If you park your bike away from main pedestrian thoroughfares then any thief that notices your bike has less witnesses and presumably more time to enact their larceny.
If you use a permanent thread locker fluid then the thief will only become frustrated and likely create more damage trying to remove the mirrors. They don't care about your property. I've seen car windows that were smashed for the loose change in a console.
Specialty locking nuts are ineffective here since the mirror's L-shape is such that it acts as a wrench when the mirrored end is used as a leverage point to unscrew the attached (threaded) end.
Vandalism is often prompted by thoughts of 'he/she has something I don't have'. Engraving or otherwise personally identifying your mirrors will only increase the likelihood of attracting a miscreant's attentions and adds the prospect of a unique trophy.
If you can live with a less-than-altruistic solution, park your bike beside someone with better mirrors that are easier to steal. Thieves are lazy. The reason that 'The Club' worked so well to deter car theft is that there was another car right next door without one.
Don't piss off anyone with your riding habits and if you inadvertently do, take the time to apologize. Spur of the moment vandalism and/or theft is easily prompted by an 'I'll show that so-and-so who's boss!' attitude that would never have erupted if you just hadn't knocked over that pedestrian or cut off that car.
Combination of theft proof screws.
These are screws which can only be removed with a special tool. There are so many different kinds that it's impractical for a thief to have all of these.
And Locktite (or an epoxy). This is an inexpensive adhesive which makes it more difficult to turn the screw.