You can take 2 out of brackets.

yes, Strings are always immutable (unchangable)

But now you do...

Wish I knew the replace method......

This solution doesn't work but was accepted for some reason... I would've modified it but accidentally pressed Submit and can't figure out how to modify it :/

I googled, and may be understood the patterns problem you mentioned. But this version is same as:
replace(char oldChar, char newChar) right?

doesen't work

dumb af

Converting the whole string to upper case during each iteration is extremely ineffective!

How do you convert a char directly into uppercase using a string method?