How do I raise the tonnage on my master of towing limited?

I have gone threw all the steps getting my license. I started with my Apprentice mate steersman. Then mate pilot, and now have a master of towing limited to 200 GRT. Where I work we only have one tugboat less than 200GRT. The other two are 265GRT.
So I’m trying to figure out how I can either get the Limited taken off my license or get the tonnage up to 300GRT. I’ve looked all over the NMC page and can’t fine what I need. So I’m hoping someone will know what I should do.

When did you get the endorsement, and why was it limited to 200 GRT? What route is it for?

I got my endorsement two years ago. I applied for the master of towing limed because I didn’t have enough time for my full masters license.
I started on deck and got my apprentice mate steersman license. Then got my mates pilots license. Then my masters limited. So I looked all threw the NMC web sight and can’t fined out how to increase my tonnage on my license. There has to be an amount of days or something I would think.

Apply for Master of Towing Vessels, not for removal of the tonnage limit. You don’t have a limitation on the Master of Towing Vessels license, you have a separate and lesser license “Master of Towing Vessels (Limited).” That may sound like it’s the same thing, but it isn’t. See 46 CFR 11.464.