How to compose regexp for Google Sheets?

Question

Regular Expressions

Hello. I ran into a problem that I can't solve.

I have a table with cell D containing phone numbers.
The numbers go in this format:

7 900 000 00 00
8 900 000 00 00

I need to make a regular expression or a formula, which I will stretch onto a plate and change the phone numbers into a single format:
8 900 000 00 00

I tried =REGEXREPLACE, because I rummage more in regular expressions, but I could not solve the problem.

Ask for help from the community. Thanks

Answer 1

=REGEXREPLACE(D1, "^7 ", "8 ")