The Google Calendar website contains a link "Need help?" that you can click to get several options to get your password back.

After you have got your password back tap "Settings", "Backup...", "Backup now" (as a security precaution) and then tap "Settings", "Accounts", tap your account and enter the correct password.

If you cannot get your password back using the method above then you have to create a new account on the Google Calendar website. However the new account will certainly be empty so you have to find a way to copy your existing events into it. Since you cannot sign in to Google Calendar any more you have your events only in CalenGoo.

CalenGoo cannot just copy your events into a different account. Instead you have to export them as an ICS file and import that file into your new Google Calendar account. After everything looks correct in Google Calendar, just change the account in CalenGoo.

To export your events as an ICS file you can tap the "i" button at the end of your calendar's line under "Settings", "Visibility/Download" in CalenGoo:


Another, but more complicated, option is to extract the ICS files from an iTunes backup: Recover