Are you trying to remove just the red corners or more than that? screenshot: https://i.imgur.com/JLKHhVf.jpg
I see from your screenshot, a layer called mask. Are you trying to use a layer mask? It is one way (a good way) to go, since it is non-destructive. Just open the image as a single layer.
For the corners make selection.
1. Select -> Select All
2. Use the rectangular select tool and click in the canvas. That sets the tool properties for the selection 0,0 for the origin and width/height same as the image. You can always set these sizes yourself if you want to.
3. Click on the rounded corners option and increase the radius value to suit. I think about 24 pixels.
Those 3 shown here: https://i.imgur.com/457sznU.jpg
(You could at this point not use a layer mask, instead invert the selection Select -> Invert and then Edit -> Cut)
4. For the mask Layer -> Mask -> Add layer mask and choose the Selection
5. Turn off the selection Select -> None
Those shown here: https://i.imgur.com/Z8GdkkR.jpg
For a layer mask: click on the layer mask icon in the layer dialogue. Painting on the canvas in Black hides, White shows, (greys give partial transparency).
Save as a Gimp xcf will keep the layer mask for further editing. Export as a png to keep the transparency created by the layer mask.
I see from your screenshot, a layer called mask. Are you trying to use a layer mask? It is one way (a good way) to go, since it is non-destructive. Just open the image as a single layer.
For the corners make selection.
1. Select -> Select All
2. Use the rectangular select tool and click in the canvas. That sets the tool properties for the selection 0,0 for the origin and width/height same as the image. You can always set these sizes yourself if you want to.
3. Click on the rounded corners option and increase the radius value to suit. I think about 24 pixels.
Those 3 shown here: https://i.imgur.com/457sznU.jpg
(You could at this point not use a layer mask, instead invert the selection Select -> Invert and then Edit -> Cut)
4. For the mask Layer -> Mask -> Add layer mask and choose the Selection
5. Turn off the selection Select -> None
Those shown here: https://i.imgur.com/Z8GdkkR.jpg
For a layer mask: click on the layer mask icon in the layer dialogue. Painting on the canvas in Black hides, White shows, (greys give partial transparency).
Save as a Gimp xcf will keep the layer mask for further editing. Export as a png to keep the transparency created by the layer mask.