I don't know what it was like back in 2016, but as of QGIS 3.10, this is implemented in in the available functions in QGIS in the expression editor or the field calculator. The documentation on the right (in the field calc dialog) gives you the solution of:

to_date( "MyDateFieldNameWithDatesAsStrings" , 'dd/MM/yyyy' )

(whitespace are optional) and hit "OK". Adapt the "format" to the one present in your attribute table. For example, if your dates look something like 07.3.03, the correct format for that would be dd.M.yy*. Pay attention to capitalization, as the symbol m stands for "minutes" and M stands for "months".

• This is not a format anybody should use. If you get a file with that format, please talk to the sender's superior. This will not stand!

I don't know what it was like back in 2016, but as of QGIS 3.10, this is implemented in in the available functions in QGIS in the expression editor or the Field calculator. The documentation on the right (in the field calc dialog) gives you the solution of:

to_date("MyDateFieldNameWithDatesAsStrings" , 'dd/MM/yyyy')

and hit Ok. Adapt the "format" to the one present in your attribute table. For example, if your dates look something like 07.3.03, the correct format for that would be dd.M.yy*. Pay attention to capitalization, as the symbol m stands for "minutes" and M stands for "months".

This is not a format anybody should use. If you get a file with that format, please talk to the sender's superior. This will not stand!