Hi Chinmay,
It is not possible to convert an existing reference field that is set to a multi-select text field. Doing that would break the relationship as a multi-select text field would no longer line up directly with a record. The issue is that your current relationship is that one team member can have many risks. You may instead want to assess your workflow and look into creating a many to many relationship. This allows for records from two tables to be assigned together to allow for many team members to be linked to many risks.
The basics of the set up would require three tables:
Team Members -> Assignments <-Risks
This way each time a single Team Member is assigned to a Risk you create an Assignment record to link them to the Risk. The connection is stored in that third table so each team member and risk can have as many assignments as you need. Then you can also create report links on Team Members and Risks to help you see how the two link up. I have linked the help topic on Many to Many relationships below:
https://help.quickbase.com/user-assistance/many_to_many_relationship.htmlI hope this suggestion is helpful Chinmay.