Adding negative flight numbers

I am using a Galaxy Note 10+ and I can’t add a negative sign to flight numbers on my discs. My phone defaults to the numeric keyboard and I can’t change it. As a workaround I use the decimal.
Anyone know how I can enter the negative sign before a number?

On my Android phone (OnePlus 8T) the numeric keyboard has a negative sign in the upper right. If you don’t have that is there something you can long press to get the option for symbols?

If you’re using the default Samsung keyboard, the dot/period key will also create the minus sign if you double tap it.

If you aren’t using the default Samsung keyboard, do you know which keyboard you are using? I believe this isn’t a uDisc issue, but keyboard related.