You'll have to change the values that begin with : to 0:
Then format Cells-Time - 37:30:55

" wrote:

26:47:00 - 1/1/1900 2:47:00 AM
:00 - :00
12:49 - 12:49:00 PM
:00:00 - :00:00
1:15 - 1:15:00 AM
:11 - :11

I have the above data in A1:A6. Text written next to "-" is how it is
shown in the formula bar. I want to convert it into [hh]:mm:ss format.

The result I want in B1:B6 is show below. How can I convert?

26:47:00
00:00:00
00:12:49
00:00:00
00:01:15
00:11:00