How to rectify a non-secure website message from Find-A-Club

I am at a lost and I've tried what I know. I was testing our website access (Southeast Houston Toastmasters-5324194) on Toastmasters.org Find-A-Club.  It generated a "Your connection is not private" message (image attached).  I got this message on Google and Duck Duck Go.  I checked another club's information on "Find-A-Club;" that connection went directly to their website.  What can I do to rectify this problem? I'm at a lost.

Thankinng you in advance,
Zenia Shipp, DTM
Southeast Houston Toastmasters 5324194
Pearland Toastmasters Club 7610

not sure what you entered into your browser but
5324194.toastmastersclubs.org/ is secure
and
sehouston.toastmastersclubs.org/ is secure

and I clicked on the find-a-club link to your site and it is secure.
sehouston.toastmastersclubs.org/

the first 5 links for you club on google for your club were secure.