If you decide to try yourself, can make it easier with a proper fid size. Get the splices as tight as you can. Use a hot knife to cut the line and use electrical tape to keep the strands tidy. When I cut line, I wrap with tape first then cut straight through the tape and line with a hot knife.
Someone at the dock could probably show you how. Used rope is harder to work as others mentioned. Wash with a mild detergent or fabric softener first. Can put in a laundry machine on gentle if you put into a pillowcase or delicate laundry bag. If you’ve only deployed the anchor a few times it should be ok still. New England rope brand is good quality - check breaking strength if you buy new.
Samson Rope Splicing Kit (Fids 1/4-Inch, 1/2-Inch)
https://a.co/d/g7N2jBw