How can I force Mozilla Thunderbird email client to synchronize and show emails that it's currently not showing?

Question

Current situation: Mozilla Thunderbird email client is showing emails from way back (year 2016) up to and including March 13, 2019, about 12pm.

After that, it is showing nothing up to March 23, 2019 7pm. Then it's showing newly-downloaded emails.

That was the time I opened up the client after the ~10 days worth of not checking email on that computer.

I will refer to the missing emails as "the gap". During the gap I was downloading the emails on my mobile phone and reading them there.

I have also checked, and all emails, including the ones in the gap, are on the server (I used web-accessible Horde client). So the emails are there! But Thunderbird is not synching them.

How can I force Thunderbird to sync all emails, including ones I have previously downloaded onto my mobile phone. Mobile phone uses IMAP and not POP3.