Fix SSL / “Your connection is not private” error

We have recently changed the hosting provider for our company website and are now receiving a security certificate error when trying to access the site.
The website is:
accountancyextra.co.uk
Chrome currently displays:
“Your connection is not private”
NET::ERR_CERT_COMMON_NAME_INVALID
We believe the issue may be connected to the recent hosting change, and potentially relates to the SSL certificate, DNS settings or the way the domain is pointing to the new host.
We are looking for someone experienced with website hosting, DNS and SSL certificates who can:
- Diagnose exactly what is causing the certificate error
- Check the DNS records and confirm the domain is pointing to the correct hosting server
- Check the SSL certificate currently being served
- Install/reissue/configure the correct SSL certificate if required
- Make sure both accountancyextra.co.uk and www.accountancyextra.co.uk work correctly
- Make sure HTTP redirects correctly to HTTPS
- Confirm the website loads normally without browser security warnings
- Avoid disrupting our email service while making any DNS changes
Our email is run separately through Google Workspace, so it is important that any DNS changes do not interfere with email delivery.
We can provide access to the domain/DNS provider and website hosting as required.
Ideally, we would like someone who can investigate and resolve this fairly quickly rather than simply advising us what needs to be changed.
When responding, please confirm:
1. Your experience fixing SSL/DNS issues following hosting migrations
2. Whether you can diagnose and implement the fix yourself
3. Your estimated timescale
4. Your fixed price for completing the work