One method based on luminance mapping:
1) menu Windows > Dockable Dialogs > Palettes (to display the palettes list)
2) select the palette in the list to make it the active palette
3) menu Colors > Map > Palette Map
Another method is to convert the image to index mode:
menu Image > Mode > Indexed...
choose "Use custom palette"
1) menu Windows > Dockable Dialogs > Palettes (to display the palettes list)
2) select the palette in the list to make it the active palette
3) menu Colors > Map > Palette Map
Another method is to convert the image to index mode:
menu Image > Mode > Indexed...
choose "Use custom palette"