Like anything

a) add instrumentation https://asktom.oracle.com/ords/asktom.search?tag=instrumentation-overhead
b) find where the most time is being lost https://carymillsap.blogspot.com/2009/12/my-whole-system-is-slow-now-what.html

The most common thing I see when PLSQL is slow is the SQL calls within it are slow, so standard tracing can also be useful

- exec dbms_monitor.session_trace_enable(waits=>true)
- run your proc
- exec dbms_monitor.session_trace_disable
- get the tracefile name from v$diag_info https://youtu.be/Xoq3lvxUTmY
- run tkprof to summarise the results