I want to switch to 46/30 but don't know how to begin. The crankset is Shimano Tiagra FC-4700, 50x34T, 170mm
The crankset (110 BCD - Bolt Circle Diameter) is unlikely to accept a 30T chainring. It definitely isn't supported by Shimano. You need a new crank.
Look at subcompact cranksets like, e.g., FSA Tempo Adventure (10/11 speed). Note that this specific one also uses a different bottom bracket.
Shimano offers the FC-RX600-10 in their gravel bike line which comes with 46/30 chainrings. The chainline is a little outboard of the road chainline (by 3.5 mm). You may be able to adjust the stops on your front derailleur to fit or you may need a new gravel one. I also don't know if it fits your bottom bracket.