@Rezzahan On the app you can't. If you don't press the arrow it's completely covered, but if you press it the blue is still covered.

You can push the stack to the right with the little arrow above it, allowing you to interact with whatever it otherwise blocks up.

Her +2 partially covers the mana selection and prevents selecting white mana.

I was playing in iPhone, and I had the same bug. When to activate Chandra’s +2 to add blue mana to cast Invasion of Amonket, but I couldn’t select the blue mana symbol because Chandra ability was in the way. When I moved it using the arrow, it was still in the way.

I'm having the same issue on Windows; when I activated the +2 the ability icon obscured White on the color wheel, which is what I wanted to select. Despite clicking everywhere around it I was unable to do so until it timed out, but I was given the White by default (I suppose because it was on top?); however my opponent had been given priority and the phase had passed causing me to then lose the mana resulting in a wasted turn which I was unable to recover from.

This has happened to me. Multiple times taking several minutes to select black mana.

This issue occurred to me, I was unable to make white mana, and it cost me a draft.

This happened to me as well but I couldn't make white.

Playing Chandra, Hope’s Beacon and activating the +2 ability:

1. On iOS the mana selection wheel is partially obscured by other UI elements. It’s particularly difficult to select black mana
2. It seems that the logic to determine whether to automatically pass my turn when I don’t have enough mana to play any of my spells is not factoring in the 2 mana added by the +2 ability. I’ve tapped six lands, played Chandra with a Go For The Throat still in hand, but my turn automatically ends after selecting the +2 ability.