If they are always in that format, with two digits for day, month and
year, then you can use this, assuming the value is in A1:
=DATE("20"&RIGHT(A1,2),MID(A1,4,2),LEFT(A1,2))
Format the cell as a date. This assumes all years will be in this
century - if you have some dates with 99, 98, 97 etc this will need a
bit of modification. Copy the formula down as required.
This assumes that years from 00 to 29 are in this century, and years
from 30 to 99 are in last century - change the 30 in the formula if
you want to make it a different break point.