SQL in Access to add leading 0 in front of zip codes

for a project I am working with a table of zip-codes that I imported from a *.csv file, exported form Excel. Those zipcodes all have 5 numbers and are formatted as text within my database. Some of them should start with 0, however during the export/import process this 0 got lost, leaving me with zip-codes that only have 4 instead of 5 digits where the leading 0 went missing. Is there a way an SQL command might add this zero to strings only having 4 digits? Thank you