Disconnect the garage door opener from the garage door, if you have an opener. Pull the emergency release cord on the rear of the door opener arm to release the arm trolley from the opener carriage just as you would do if the power went out. This allows you to operate the door manually.
Raise the garage door to the fully open position. The bottom edge of the garage door should be in the curve of the track. The sides of the weatherstrip channel should be visible.
Insert a flathead screwdriver into the weatherstrip channel, and twist the screwdriver handle to expand the end of the channel. The channel is crimped to hold the weatherstrip in place. Grab the end of the weatherstrip with a pair of pliers and pull it out of the channel.
Apply a thin film of liquid dish soap to the "T" on the T-bulb weatherstrip with your fingers. The dish soap should be on both sides and the top of the "T" to enable the weatherstrip to slide into the channel.
Insert an end of the weatherstrip into the open end of the channel. It is helpful to have an assistant hold the uninstalled weatherstrip level with the garage door bottom as you push the weatherstrip into the channel.
Grab the end of the T-bulb with your fingers once it is in the channel at least 3 inches. Carefully pull the end down the channel as your helper "feeds" the T-bulb from the open end. Once the T-bulb weatherstrip is in the channel fully, crimp the open end of the channel together with a pair of pliers.
Close the garage door and engage the door arm trolley with the opener carriage until it locks into place.