How do I fix this?

Melanie • I'm Melanie(27) & mommy to 3 precious boys 👬👶💙 Currently trying for baby #4. Our final precious addition to our Fam❤️
So for some reason when I logged on today it had moved my period from starting on the 25th to starting today... and it won't let me fix it... how do I get it back to normal?