Hello,
you could do it as follows -
pretrained_model = torchvision.models.video.r3d_18(pretrained=True)
modules = list(pretrained_model.modules())

pretrained_sequential = nn.Sequential()

for _, module in enumerate(modules):
    pretrained_sequential.add_module('module' + str(_), module)

You can decide up to what layer you want to add into to your sequential block. For that you might want to see how ResNet3D is implemented in torchvision