One-Time SEO-Optimization needed

Hello,
I am looking for someone who can help me with a one-time SEO-Fix.

Seobility tells me: Technic & Meta: 50% | Structure: 90% | Content: 48%

I want at least bring Tec & Meta and Content also to green area :)

I am looking for someone, who will also help me understand, so that I can work on it in the Future.

Since my website is in German, I prefer a German-speaking person.

Check website: https://digilexpert.com/

Looking forward to your proposals.