Steel shot bags can be used to apply force to a screen assembly during reassembly to ensure a good adhesive bond. iFixit carries a 30 lb steel shot bag as well. Ruck weights can also be used for the same purpose.
While iFixit carries several options, it may be best to source these locally to save on shipping costs or from other companies that are setup to deliver products like this better. For more sourcing ideas, please check out our Weights for Screen Reassembly wiki.