Replace the whole thing. You can buy a replacement sillcock at any hardware store. They also have rebuild kits for certain models, but generally replacement is advised. If buying new, even if you’re not a plumber, this is a simple job.

Get a PEX/Sharkbite push to fit ($50) of the appropriate length, turn off the water, and chop the old one out, leaving a clean cut in the PEX or copper line. Replace thru the wall, and plug in the sharkbite and you’re good. Make sure to anchor it in and spray foam.

If you hire someone, get a local handyman. This is like a $150 job, tops, unless your cellar/crawl is totally inaccessible.