Changing SD card from external to internal

Disclaimer: This is my experience, do this at your own risk. I did this moving from Android 7 to 10, but it should work fir you on 6.
First make sure Google backup and restore is on for all apps and data. Wit while it syncs the phone with your google account. when that's finished power the phone off and remove the SD card. now insert a new card of the largest capacity that the phone supports. turn the phone on and format the card as internal storage. Now factory reset the phone and log back in to your Google account. make sure that automatic backup and restore is turned on. Google should ask if you want to restore from the phone. say YES and all apps and associated data should be restored.

I used this process to back up everything from my old Android 7 phone and restore to my new Android 10 one. Everything was correctly restored, Apps and data, including a 3rd party launcher and wallpaper.

 

just keep in mind that this will cause wear and tear on the sd card. so be prepared for card failure, the older the card gets.....so backup your important stuff regularly. i would recommend you use google photos to backup your photos as well.