Hello and welcome to Gimp Chat.

You can use "Change Image" to create a GIMP gradient from the button. Then use that gradient on linear to fill the area of the button. Get it here attached.
Attachment:
Change Image.zip [720.5 KiB]
Downloaded 412 times
Unzip to the desktop or a new folder on the desktop and double left click the little pencil icon to open the welcome window.
When the window opens click the welcome window and the program will open. Open the image in it and create the gradient by drawing on the image. Example.

Then just click the little floppy drive icon to save the gradient.
Open GIMP and load the new gradient. Make sure it's set to "linear"
Open your target image you want to change.
Create a new layer with a name like new button or something like that on top.
Make the new top layer active. Use the free select tool to select the button area you want to fill with the gradient.
Using the gradient tool create the new gradient fill over the old button within that selection.
Then create your text and use the perspective tool to get the correct angle and depth.
