I didn't feel like typing too much so here's a good link...
https://carroar.com/bass-blockers/
Scroll down to the part about "How to make your own" - generally speaking you need to know A) what frequency you're trying to cut at and B) what impedance your speakers are at. There are various calculators and charts on the interwebs that will tell you what cap value you need to achieve that. Sometimes the common sizes are not where you'll want things to be.
Additionally, I'm going to presume you're using the OEM headunit and not aftermarket or an amp. In alot of cases, you can cut the frequencies you're after if you are.
