Assuming
- your project prefix is
EXAMPLE
- your JIRA installation is at
https://example.com/jira
then regex to match is
(EXAMPLE-(\d)*)
if you want to match all text that looks like a JIRA, and not hardcode EXAMPLE
, then you can use
([A-Z]*-(\d)*)
then the replacement is
[$1](https://example.com/jira/browse/$1)