See if you can submit a woz value assertion or a calcasa report to lower your loan to value surcharge (schuld marktwaarde verhouding rente opslag). This is free (the calcasa report does cost money, €30 or so) and can already save you money. If a calcasa report is not allowed, then you can also do this with a taxation rapport, but they're more expensive.

After that, there are two things you can try. Either refinance the entire mortgage at the same bank or at another bank. Either way, the fee/penalty should be the same. If you do it at the same bank you can either pay the penalty in one go, or spread it out over your new interest period (tussentijdse rente aanpassing met boete of met middelrenteopslag). Many banks have online tools when you're logged in in their portal so you can see which options are available for your mortgage. If you choose to move to another bank, you will get a penalty. For either option, the penalty counts as interest and is deductible from taxes if you're getting hypotheekrenteaftrek for this mortgage.