Fixed interest rate KfW loan expires

Dear people, I received mail that the fixed interest rate on our KfW loan for our semi-detached house is expiring (10 years, it couldn't be longer). To be honest, I had forgotten that because our main loan has a 20-year fixed interest rate and I was distracted by patting myself on the back about what a smart fox I was. The remaining debt for this is approximately €28,000. Now I'm considering the following options: Let the loan continue to run at the supervising bank for 4.2% (lazier option