I have a Rockrider btwin 6.2 full-suspension mountain bike. After 3 years of use, most of the parts were shot. I replaced most of them but also noticed that the swingarm pivot seems to have a seemingly unsafe amount of play. It surely seems to move more than 3-4mm. Before i try to open than and see what's up, is there anyone who has had a similar problem? or who know whether the bearings are standard/available and if at all it's easy/possible to fix it? considering this isn't a very expensive mountain bike. Would still like to keep it though, serves the commute to office and the outdoors on weekends. Thanks.
First thing to do is check all the pivot bolts are tight. If that doesn't fix it, figure out where the play is. Is it in the swingarm pivot, or the shock bushings? You can figure it out by holding onto each joint in turn and moving the swingarm. You shoukld be able to feel which part is loose. If it's been like it for a while, it might be all three points.
Once you find the source of the problem, I guess you'll need to go to your local bike shop (or the place you got the bike - Decathlon?) and see if they're able to source the spare parts. Shock bushings should be easy enough to get, but I don't know about the pivot hardware. You'd need to open it up and have a look what's in there!