32 bit and 64 bit

While building a simple application, I had the “App not optimized for your Mac” warning which, according to Apple is due to the app running in 32 bits.
Maybe a silly question: is it possible and, in case, how do I convert my app to 64 bit?

Thank you

Compile it to 64Bits using Xojo 2018r1 (or previous but capable version) ?

IDE - left panel - build settings - MacOS
Then select 64bit in the inspector panel

Thank you everybody

Be sure to read the developers notes on 64 bit: http://developer.xojo.com/64-bit-guidelines