Already discussed at https://www.duolingo.com/comment/26763151 , please read first.

1. Your translation must be actually used in the target language.

2. Dobré ráno, not Dobrý ráno

If you look above you can see that Dobré ráno is the official translation here.

Dobrý is masculine, ráno is neuter. Dobré is for neuter.

This is really a question for the vendor of your keypad. Find such a virtual keyboard where you can switch languages easily. I can't even recommend any, because you did not even tell us what kind of phone you have.

Andriod phones will allow you to select the right option. For example, try this - go to your phone's keyboard and tap on the vowel "i" and hold - a pop-up will appear above the letter "i" - you should see a variety of accented versions of that letter (ï, î, í, ì, ī). Move over the one you want and lift your finger off the keyboard. The selected letter will appear on the screen. Hope this helps.