A warm welcome to Mac-Forums.
It's while since I used iPhoto as it was replaced by the Photos app some considerable time ago.
But, assuming you imported the videos into iPhoto in the first place; the first thing to do is open iPhoto.
Now look to your left. This is the Sidebar and listed are are your Folders, Albums, Dates and so on.
Look down the list for any of the following words: "Videos"; "Movies".
You may have to open the disclosure triangles to see the contents of your Albums etc.
You should be looking for something like this - NB these screenshots are taken from Photos app so there may be slight differences.
View attachment 28944
View attachment 28945
Please let us know how you get on.
Ian