@Kanapali Thanks for reaching out!
We have a quick clarifying question: when you are referring to the 'fork suspension lock/unlock button' are you talking about the switch on the top of the fork (likely a blue color on the right fork arm) or are you talking about a button located on the handlebars, similar to a gear shift button, that would allow you to lock the shock?
If it is the switch on the top of the shock that you are missing, then you'll want to contact the store and speak with a bike tech. If they are able, they can do a contactless pick up curbside to get the part put on. From what we can see, it does not appear that the Cannondale Althea 3 has a button on the handlebar to lock out the shock (referred to as a 'remote lock out').
Hope this helps!