gin index

how would I indicate this index exists on my prisma schema...

 CREATE INDEX ON my_table USING gin (my_string_column gin_trgm_ops);

 CREATE INDEX ON my_table USING gin (my_string_column gin_trgm_ops);

 CREATE INDEX ON my_table USING gin (my_string_column gin_trgm_ops);

 CREATE INDEX ON my_table USING gin (my_string_column gin_trgm_ops);