Format number of Six characters since data set with differet format and add 0 before

Hello,

i would like to omogenize my table in this way, having a format number of six characters.

My starting table have a lot of record of 4/5 characters and i would like to add “0” in front of the different cases.

For example the code “1309” must become “001309” or the code “15011” in “015011”,

Which kind of node or expression in “String Manipulation” can i use?

Thank in advance for every suggestion.