In Islam, circumcision is not obligatory, and it is considered as a Sunnah, strongly emphasised on, especially at a young age. This means that being circumcised or performing circumcision is not a necessary condition for converting to Islam or being a Muslim.
For any male, whether Muslim by birth, or having converted to Islam, who has not undergone the process, they should consider doing it, as there are many religious and physical benefits for it.
Some of our esteemed jurists do consider it to be obligatory for a Muslim male to undergo circumcision whenever they can, if they were not circumcised when they were young. However, if a man wishes to perform his Hajj pilgrimage, one of the obligatory prerequisites is that he must be circumcised in order for his pilgrimage to be valid.
In any case, please refer to the specific view of your Marja' taqleed in this regard.
And Allah knows best.