Temporary relation files not removed after sessions ends - Single PostgreSQL instance PostgreSQL 13

We are facing default temporary tablespace disk space full issue due to lots of below temporary relations files created but not removed after ending session

1.1G    t756_1536213694.409
1.1G    t756_1536213694.410
1.1G    t756_1536213694.411
1.1G    t756_1536213694.412
1.1G    t756_1536213694.413
1.1G    t756_1536213694.414

Please note: - these files are not in pgsql_tmp <-- this is used for temporary files like sorting etc. these file are created in temp_tablespace location which default tablespace currenlty.

spin=# show temp_tablespaces ;
 temp_tablespaces
------------------

(1 row)

I tried to get the backend id from below query but no luck as process id is changing every time when execute the below query .

spin=# SELECT bid, pg_stat_get_backend_pid(bid) AS pid FROM pg_stat_get_backend_idset() bid where bid='756';
 bid |  pid
-----+-------
 756 | 41533
(1 row) 
 spin=# SELECT bid, pg_stat_get_backend_pid(bid) AS pid FROM pg_stat_get_backend_idset() bid where bid='756';
 bid |  pid
-----+-------
 756 | 86639
(1 row)

Questions: 1. Can we remove directly ?
           2. are these files are removed once db restart ? 
           3. How WE CAN find which session created these temp relations which is not get removed once session ends ? 
thanks for your help.