OK I know that image, its based on openatv, which I have. The following is the easiest way.
1. Set dish at new elevation BUT mark it first to show correct one for 28east.
2. The elevation for 19e is say for high wycombe is 28, for sky its 25 so dish goes up mark new one. Dish is now ok. Check dishpointer for your exact location.
3. You select 19east and save.
4. Loosen dish fixings slightly.
5. go to signal finder and enter a signal frequency that is a known 19e astra channel, use bbc europe 11229 etc but it has to be coorrect ie dvd-s2, vertical, 8psk, 2/3.
6. For this bit you need either 2 people or be able to see signal finder, move dish slowly to right and in less than one minute signal bars will fill BUT digital has a slight delay so pause.
7. If you have a smartphone you can download an app that will show exact direction for 19e, you leave it on LNB. Did I say LNB!! Ah yes, the skew for 19e is different for 28, but you may get a signal with existing skew. The skew for 28 for HW is 13.5 and for 19e its 7.6.
8. when you get a signal , BBC should be around 80-90, do a bit of tweaking ie move elevation, adjust skew, tighten up you can now scan etc. And you could plug in signal meter and it may now work as it actually has a signal.
I know you said you did it before but can you remember the 28e frequency you were using and did you leave dish as is? And did you just see a signal for 19e or an actual channel?