Will I be able to catch up any day I missed finding a robin or have I spoilt my lights

You can go back a day at a time, when the door is closed.

how do u change ur mushrooms lights, seen a white and red lil cutie one, mine are red mostly and  i have one yellow at mo

You can only change the lights to colours you've earned for that day - each of the wildlife for the day that you spot unlocks another colour until your 8th spot unlocks white (the order is red, orange, yellow, green, blue, indigo, violet, white).

If you've unlocked different colours you can edit them by clicking the calendar, clicking the Edit Fairylight Colours link, then clicking the light you want to change.  Keep clicking, and it will rotate through the colours you've unlocked.  When you get to the one you want, hit the green Save button.

Tracey can I go back after as I have an unlit fairylight

Tracy how to check which light is which day ? I need to come back and get more colours but. I have no idea which day it is

1 is the central one,  then  it alternates between the left side for even numbered days, and the right for odd.  So immediately to the left of centre is day 2,  immediately to the right of centre is day 3, and it continues outwards like that :)

Thanks Tracy . Now I need to go back to day 5 to get the yellow light . How do I do it

When the door closes, click it, and there's a link to go back a day.  Click that until you are back at the day you need :)

No i can move  only 1 day back Tracy...no further