Bambu labs omfg how do i start

Where do I start in the picture you can see it is a circular object so in bamboo Labs I opened up a new project I inserted a circular object but I cannot work out how to change the length and the high of it and then make the extra for different dimensions on it then I have to do this little clip top on one end and the same on the other end you can see the length roughly that I need to do it the thickness is what I need to measure and unfortunately the caliper hasn’t come yet to test and get the exact size so how do I change these dimensions in bamboo Labs it’s really getting on my nerves but it’s early days

As you can see from the bottom of the picture the white stuff is the glue where I’ve tried to repair the original item and that section needs to be strong