Can I adjust the contributions for my self-employed pension scheme?

Yes, entirely. You decide how much you contribute, when you do it and whether you want to pause temporarily. Pausing is free and you can resume at any time.

That helps with fluctuating turnover: less in quiet months, an extra deposit after a strong quarter. You arrange it in the app. Do keep an eye on your jaarruimte, so you don't contribute more than is deductible.