You will need to add webhooks in Jira that make the calls to Servicenow's SOAP API (although I didn't think it had one, I thought it only had a REST one), or write code with a scripting or automation app that can make the SOAP calls.
We can't tell you a lot more than that. "Integrate" does not tell us what you are trying to do.
Assuming you have Jira of hosting type "on-premise" (on your server, Jira Software Server or Jira Software Core) there is a marketplace connector which you could check further.
While I haven't seen it so far and I am not affiliated with them it sounds it could get you started faster than having to write a whole integration on your own:
In case you are using Jira cloud this does not apply, however.
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