1x vs 3x crankset

You do not say which 3x crankset you have, so first thing to check is if the chain rings are bolted or riveted. If they are riveted then it is a new crankset to go 1x.

If they are bolted and you can remove them, it is then a case of deciding do you need a new chain ring or different size. If you need a new chainring then look for a narrow wide for better chain retention.

For chain line, from 3x you would normally put the single chain ring in the middle position on the spider.

Does your rear derailleur have a clutch as that will also assist with chain retention, but if you do not fit a narrow wide, you may also need a chain retainer. A lot depends on the type of riding which you do, as to how likely the chain is to come off.

Once you remove the two chain rings, you can also then remove front derailuer and shifter and you may also need to resize your chain.

Google is your friend eg https://www.bikeradar.com/features/how-to-convert-your-bike-to-a-1x-drivetrain/