Spell the modes

Starting a scale on a different degree changes the sound completely and the spelling not at all.

D major is D, E, F♯, G, A, B, C♯. Start it from the 3rd and you get F♯, G, A, B, C♯, D, E — the very same seven names, rotated. Nothing is added and nothing is respelled.

That is worth holding on to: a mode is a rotation, exactly like an inversion is a rotation. If you can spell the parent scale, you can spell every one of its modes.

Same seven names, starting somewhere else

D major from the 3rd: F♯ G A B C♯ D E — the same names as D major.

Practise this in the trainer — it opens with this lesson the first time the concept comes up.