From the GSW Website, here are the use and application of these new items. I used them on my review build of a Supermarine Spitfire and you can see the results.

GSW Decal Fixer helps the application of decals onto surfaces of models, miniatures and dioramas. The GSW Decal Fixer prepares the surface with special agents that soften the solvents of modern paints making decals more resistant and glue stronger. In addition, the decal fixer makes the decal more flexible and increases the adherence, preventing the silvering effect.

Decal Fixer

Content: 1x 17ml bottle

Instructions

1. Before applying a decal to your model, apply a bit of GSW Decal Fixer to the surface of the model where you are planning to set your decal. GSW Decal Fixer protects the paint beneath and smooths the surface, thereby helping to prevent silvering. Use a paintbrush to gently push the decal off the sheet and onto the model. If it is hard to move the decal around, adding bit more GSW Decal Fixer or water will help the decal float on the surface until it is positioned correctly.
2. If the surface where you want to apply the flat decal is curved, like a shoulder pad, your decal could become wrinkled. To avoid this, once your decal is in place, apply GSW Decal Softener. Let the softener react and it will help remove wrinkles, as it adapts to the curved surface underneath. Repeat this step 2-3 times till wrinkles are removed.
   
   Remove any excess with a cotton swab to remove the liquid caught between the decal and the surface. Roll the swab over the decal so it does not lift from the surface. You can also use a paper towel to press down on the decal in a rolling motion to remove the excess of liquids. By using GSW Decal Softener the relief cuts to remove wrinkles in your decal will not be needed.
3. Finally apply GSW Decal Fixer again to the decal and the surface of the model where we have been working to unify the surface. Coat it as normal with matt or gloss varnish if you consider it necessary to remove or add a glossy finish.

Decal Softener

The GSW Decal softener is the solution for the application of decals on uneven or rough surfaces.
It completely softens the decal to allow it to adapt and be perfectly fixed to the surface of the model in order to avoid the appearance of wrinkles, and in this way, you can obtain perfect results that otherwise would be impossible.

Content: 1x 17ml bottle

Instructions

If the surface where you want to apply the flat decal is curved, like a shoulder pad, your decal could become wrinkled. To avoid this, once your decal is in place, apply GSW Decal Softener. Let the softener react and it will help remove wrinkles, as it adapts to the curved surface underneath. Repeat this step 2-3 times till wrinkles are removed.

Remove any excess with a cotton swab to remove the liquid caught between the decal and the surface. Roll the swab over the decal so it does not lift from the surface. You can also use a paper towel to press down on the decal in a rolling motion to remove the excess of liquids. By using GSW Decal Softener the relief cuts to remove wrinkles in your decal will not be needed.