Defulted Email Subject Line "Date"

After creating a new Agenda and opening the emailing center, the "Email Subject" line reads, "9505 Crossroads Toastmasters Club Meeting Agenda for February 1, 2024", as it should. I now select "Email Tools" choose the email templet I've created a templet.  After loading my templete and "Confiring", the "Email Subject" date changes to another earlier date which now reads, "9505 Crossroads Toastmasters Club Meeting Agenda for August 17, 2023." 
What can I do to fix this? 

Just over type over the subject line.

There is no link between email templates and agenda.

For Agenda you should be using the agenda email tool at the top of the agenda.

When you save a template, you can optionally save a header with it (as opposed to a description)
If you do want to use a stored template message which has a header, you will get a message when loading the template asking if you want to 
"Overwrite current email subject with template subject".  If you choose no, the current header will be used, otherwise the template header will be used.
Either way you can override by typing your required header in the subject line, as Brian has explained

If you want to remove the header from the template, just save the template again with a blank header.