How can I raise RMS in GarageBand or Logic Pro for ACX?

How can I raise RMS on GarageBand to comply with the ACX requirements for an audiobook? Or in Logic Pro?

RMS gives me the warning: "RMS is too low. Raise the level of this file 1.3 dB."

I used GarageBand for 20 years, but 3 months ago I switched to Logic Pro because I needed a higher resolution file for a Text-To-Speech project audition. Then I recorded a whole book for ACX with Logic Pro. But nobody - Not Apple Support, and not ACX experts in Facebook Groups - Can show me how to raise the RMS. I found a video saying it could be done in GarageBand, so I exported an aif from Logic Pro and imported to GarageBand, but I'm following all the video steps and I still get the warning on ACX.