import re
my_list = ['','2022-03-31', 'euss', 'projects','2021-03-31']
result = []
rx = re.compile(r'(\d+)-(\d+)-(\d+)')
for i in my_list:
    if rx.search(i):
        result.append(rx.sub(r"\3-\1-\2", i))

print(result)