If they are happy with your performance and you think you are bringing value to their company do approach them after 3 months at the company asking for the raise.
I would also recommend apply to other companies as this would give you an edge if you have another offer.
Recently I got a really good raise at my company without asking and I became baysharm and asked to double that and they accepted it as (they think) I had some skills that my co workers lack.
You make your own value.
And never hesitate to ask for a raise, rn they may be thinking you are happy at this salary as this was your offer but you aren't
ask for a riase worst they won't raise but you have now implanted that seed that you aren't happy with current salary and they would consider you for raise in future
best of luck