SSIS Get the highest ID number and assign ID to the next records

Hello

I'm developing a data warehouse for a vet treatment database.

I need to assign an ID column when a Pet has stayed in Hospital.

In SSIS I need to get the max ID from the ID column, which I know how to do. I thought I would run a Max SQL script and assign it to a Variable.

How do I take that Variable and add one for each record for each Pet that has stayed in Hospital?

Regards

SQLSearcher99