From the Principals list kebap menu next to the remove button

Kebap menu:

https://www.figma.com/proto/h2HxCPmleg9x1IMfPbCJrd/Infinispan?page-id=132%3A13700&node-id=164-23876&viewport=471%2C-347%2C0.1&scaling=scale-down&starting-point-node-id=167%3A21894

And from the button Principals detail page

Button:

https://www.figma.com/proto/h2HxCPmleg9x1IMfPbCJrd/Infinispan?page-id=132%3A13700&node-id=167-19921&viewport=471%2C-347%2C0.1&scaling=scale-down&starting-point-node-id=167%3A21894

open a modal to add/remove roles to a principal

https://www.figma.com/proto/h2HxCPmleg9x1IMfPbCJrd/Infinispan?page-id=132%3A13700&node-id=189-24945&viewport=471%2C-347%2C0.1&scaling=scale-down&starting-point-node-id=167%3A21894

Use these two REST API calls:

https://infinispan.org/docs/stable/titles/rest/rest.html#rest_v2_grant_principal_roles

https://infinispan.org/docs/stable/titles/rest/rest.html#rest_v2_deny_principal_roles