The only way Rodrygo can do this is to give his best performance when given the opportunity by Alonso. If he can make a bigger difference when given the opportunity, perhaps Alonso will start considering him as a first-team player. But if the results are the opposite, he will certainly remain a substitute at Real Madrid, so Rodrygo must make the most of this opportunity and take it very seriously to prove himself as the best on the Real Madrid team. However, it is clearly not easy for every player because in the Real Madrid team there are also other best players in every line.
Real Madrid has many forwards at a much better level than Rodrygo, making it a bit more difficult for him to break into the starting lineup. However, I'm sure Xabi Alonso will give him a chance, even if it's not as a starting player, because next season Real Madrid will play many matches, so players will be needed to fill certain positions. When he gets that chance, it will be a chance to showcase his individual qualities, and Rodrygo will gradually become an important part of the squad. Patience is the key because if you don't want to go to another club, what you need to do is improve your quality to be better.