Golang how to replace string in regex group?

I want to replace strings:

"hello [Jim], I'm [Sam]" to "hello [MR Jim], I'm [MR Sam]"

"[Greetings] hello [Jim], I'm [Sam]" to "[Greetings] hello [MR Jim], I'm [MR Sam]"

How can I do this via golang regex?

re := regexp.MustCompile(`hello [(\w+)], I'm [(\w+)]`)

Thank you very much!

If you have a para from which you need to identify the string then may be you could use two regex to achieve it:

namePattern := `\[(\w+)\]`
replacerRegex := regexp.MustCompile(namePattern)
finderRegex := regexp.MustCompile("hello " + namePattern + ", I'm " + namePattern)
fmt.Println(re.ReplaceAllString(re1.FindString("hi hih hi hello [Jim], I'm [Sam]"), "[MR $1]"))

https://go.dev/play/p/kv6CfTv0-sk

EDIT:

simple way to retain other part of string (PS: can be optimized and need checks for edge cases)

str := "pre string hello [Jim], I'm [Sam] post string"
namePattern := `\[(\w+)\]`
finderRegex := regexp.MustCompile("hello " + namePattern + ", I'm " + namePattern)
replacerRegex := regexp.MustCompile(namePattern)

// string part subject to replacement
str_rep := finderRegex.FindString(str)

// array of string holding the pre and post part ( check for str_rep as it could be empty)
strPart := strings.Split(str, str_rep)
replaced_str := replacerRegex.ReplaceAllString(str_rep, "[MR $1]")

// concat to get the final string (implement checks for edge cases)
finalStr := strPart[0] + replaced_str + strPart[1]
fmt.Println(finalStr)