Most posts allow editing for approx 1 hour.
If you need to edit after that window has expired you can contact a moderator in one of 2 ways...
click on the "Report Post" triangle at the bottom left of the post and request a mod enable edit or
Click on any mod (bold username at the bottom of the main TF page) send a PM and provide a link to your post requesting they allow you to edit.
I tried to find your post but couldn't find it on the For Sale section?
[Edit} found it in another section and enabled edit for you.