Taking over my family business's website. How do I tell if it was indexed with Google?

I'm finding that my family's website is ranking really badly so Im doing what I can as a complete beginner to boost our SEO. What I'm seeing is that submitting our sitemap to Google for indexing is a pretty key step that I'm wondering if it ever got done. How do I check that this has been done and are there negative consequences to me doing it again through my own Google console?