How to remove the "border" that defines the object in an imported transparent png?

[kanihoncho]

In photoshop an imported transparent png does not have an "object border". AP does and it prevents me from coloring the object. It is multiple colors and I want to fill it completely with black. When I try to color it the entire "border area" fills in with black and not the object of the transparent png. I can't find a way to accomplish this. Is there a way to eliminate this "border" that is defining what this image is?

[NotMyFault]

1. Activate “protect alpha”
2. use channels panel, uncheck “editable” pencil symbol on alpha channel 

dont forget to activate again when done.

 

https://affinity.help/photo/English.lproj/pages/Panels/channelsPanel.html

Edited May 9, 2022 by NotMyFault
Slightly edited to increase clarity

[kanihoncho]

I'm not finding any "lock alpha" anywhere. AP search reveals nothing either . . . only a "protect alpha" in the brush context menu at top which is unchecked. there is also no "edit " to uncheck in the channels panel . . . using AP v 1.10.5

[kanihoncho]

I duplicated the layer and it somehow allowed the selection tool to now enable the Edit>Fil with primary color to appear and work. Don't know what duplicating the layer has to do with this, I was unable to use the fill command before the duplication as it was greyed out . . .

[NotMyFault]

3 hours ago, kanihoncho said:

I'm not finding any "lock alpha" anywhere. AP search reveals nothing either . . . only a "protect alpha" in the brush context menu at top which is unchecked. there is also no "edit " to uncheck in the channels panel . . . using AP v 1.10.5

I updated my post for additional clarity.

yes, protect alpha in brush panel (and many adjustments and filters) is the way to go.

In channels panel, the “editable” flag is symbolized by the pen. 
 

So both options are available, sorry for lack of precision describing them.

Help and tutorial videos cover how to use them.