How do I remove window sill stop block on double-hung vinyl window?

The vinyl double hung window was installed on my brick house a few years ago. The Screws that hold the replacement windows are drilled in through the bottom of the drain holes with no caulking on the screw heads. Now there are rusted screws and water leaking in home and has molded inside walls. Walls have been torn off and mold remediated…

The question I have is how do I get to the screws to replace and caulk? I don’t want to break the bottom sill stop but I don’t know exactly how to "pop" it off. I feel like I can pull it up a little bit but don’t want to snap this plastic and destroy integrity of window.

I didn’t own the house when the install occurred, but no caulk on window screws is a huge workmanship error in my simple mind. I only can reach one of the screws with my hand and screw head is rusted with no caulk in sight.

Any assistance is much appreciated…BTW I have the exact set of windows 5 more times around my house so this may be a much needed process if this is the same procedure used on each set.

Here’s the overview of the situation:

Here is a closeup of a leaky screw:

Here is the window sill stop block

Here is that window after removing the stop block: