You can do this with just replace in Kotlin:
"foo and foo".replace("foo", "bar") // "bar and bar"
Note that the call above replaces the literal strings, if you need a Regex as the first parameter you can do either of the following:
"foo and bar".replace("[abcd]".toRegex(), "x") // "foo xnx xxr"
"foo and bar".replace(Regex("[abcd]"), "x") // "foo xnx xxr"