Transition from potty chair to adult toliet?

So my daughters got the potty training down good, except they only use the potty chair only, they afraid of toliet even thou i bought then the dora seat to put on top of toliet seat and it has handles. My daughters do well all day on potty chair. Their little under 2 and bit small and my toliet is little high. What should I do, i want them to get used to using toliet because in case if I go out to public or other people's house. I carry their potty with me to their grandparents house. Any advice. thanks