Is the old tubing in place? You can use it to drag the new one through up to the dash.
Now they are not all that accurate, so if you do not have a gauge already in the dash for such? Your Sounder / GPS would also give you speed information OR you can download a free app for your Smartphone that will give you GPS based speed.
There are also GPS based speedometers that you can install in your dash as a replacement unit.
Lastly, if present now, if the hose is not broken or leaking? I would 1st check the tiny hole on the lower unit to make sure it is just not plugged 1st?
Another simple fix for me and this video should help you with yours ;) And was Salt Water crud left over in my case, and it is a tiny hole for sure so it would not take much to plug it up! Helpful I trust? Dave