Figma 2D PNG or SVG inverse help / working plugin?

Hi,
I have a simple png image, like a blob.

I want to have the outer part of the where the blue X are at all be a new image or PNG, and the original blob will be transparent background, or not part of the new shape.

I have tried CTRL SHIFT A and it does nothing.
I have tried the plugin ‘Select Inverse for Real’ and it does nothing.

Can anyone tell me how I can do this?

Thanks

Maybe I am using the wrong word, I want to create a reverse image of the blob.

Where the X are at, would then be grey and the current grey blog would be transparent

Hello,
Thank you for the reply.
I just started using Figma… Love it and all the plugins!