To deal with infinite DLMs, we can use the Koyck transformation. When we apply Koyck transformation, we get the following:
$$
Y_{t} - \phi Y_{t-1} = \alpha (1-\phi)+\beta X_{t} + (\epsilon_{t}-\phi \epsilon_{t-1}).
$$
When we solve this equation for \(Y_{t}\), we obtain Koyck DLM as follows:
$$
Y_{t} = \delta_{1} + \delta_{2} Y_{t-1} + \delta_{3} X_{t} + \nu_{t},
$$
where \(\delta_{1} = \alpha (1-\phi),\delta_{2}=\phi,\delta_{3}=\beta\) and the random error after the transformation is \(\nu_{t}=(\epsilon_{t}-\phi \epsilon_{t-1})\) (Judge and Griffiths, 2000).
Then, instrumental variables estimation is employed to fit the model.