Help with external corner please

[Nut]

The gap in the top tiles is bigger than the bottom. Mitering the corners would enable you to get an even grout line on the corner.
A smudge of caulking over the top of the grout at the top of the tiles will give you a smoother transition and nicer surface to paint. Fila Deterdek or similar will get the excess grout from the surface of the tiles. The silicone should be a constant angle, yours is in and out, thick and thin.

Thanks. Would you take the grouting off the top of the tiles where it meets the wall before putting the caulk on?

it's too late for trim unless you remove tiles

Thanks Tony. I would take off the corner tiles to put the beading in.

 

[Time's Ran Out]

As it’s just a holiday let I’d just get a bit of aluminium angle and stick it over the corner.

 

[WetSaw]

If you're going to remove the tiles you might as well mitre the tiles and do it properly, otherwise what TJ has suggested will do the job ( as it's only a holiday let )
No need to remove the grout at the top of the tiles unless it will leave you an uneven surface to paint.