Quick solution that maybe can help someone, in my case, @ini_date is a parameter, so query conversion was not applicable....
When a date is in this format -> yyyymmdd, I 'constructed' a valid date string, with right() mid() and left(), concatenate it with slashes, and then convert it to date type, so it can be formatted.
Here's the expression>>
="Date: "&format(cdate((right(Parameters!ini_date.Value,2) &"/"&mid(Parameters!ini_date.Value,5,2)&"/"&left(Parameters!ini_date.Value,4))),"MMMM dd, yyyy")
just replace the "MMMM dd, yyyy" part, with whatever fits your report the most.