How to write characters containing the ǚ pinyin symbol in most common Chinese Input Methods?
As pinyin doesn't use the letter v, then words containing the u with umlaut can be written with v key, then combined with the number keys to get different tones. 

For example: 


v+1 = ǖ
v+2 = ǘ
v+3 = ǚ
v+4 = ǜ
v+5 = ü