Hello @AnnistonSmith
There could be a number of things blocking you from taking a test on lockdown. What type of computer are you using? Have you downloaded it this semester or have it from a previous semester? You should try deleting it completely and re-downloading it first.
If you are still having an issue, confirm with your teacher it is actually open for students to take. Sometimes there are lock out dates or passwords that teachers or students are unaware of. Is there a particular message you get or what isn't working?
You can also speak with Lockdown Browser directly:
https://web.respondus.com/contact/
As a last resort, you can also speak with Canvas Support who can take a look at the specifics with you.
https://community.canvaslms.com/t5/Canvas-Basics-Guide/How-do-I-contact-Canvas-Support/ta-p/389767
