So not a request type at all, but a link to another page.
You should remove the "other concerns" request, and then customise the screen to have your link. Natively, the portal does not have a way to do that, but you might be able to do it with refined themes.
You want a link to another page on this page.
You initially said you wanted to replace the "other request" option in the list with your link.
The "other request" option is an entry in a list of request types, it is not a link. But you don't want it, so
Action 1: Remove "other request" from the portal list of request types - you don't want it there.
To get a link added to the page, you will need to amend the code that provides the page, adding your link to it. This is not possible in plain Jira Service Management, but may be possible with an app that themes it. I've suggested Refined as it's the only one I've used (there may be others). So,
Action 2: Look at theming to see if it can inject the code for the link you want
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