I don't always have a problem with motivated cognition, but when I do, my brain usually makes it some or all of the way through the following steps:

• Notice that I'm becoming more comfortable with (feeling safer about) a decision or action I'm about to make or just made.
• Notice that the physical cause of my comfort is that I recently had a thought consisting of a reason the decision could have a good outcome.
• Some brain process that I haven't pinned down yet that feels like and possibly is a mix of noticing optimization by proxy, feeling disdain for non-generalizable reasoning algorithms, and wondering about the true component strength of the reason.
• Apply my bullshit detector to my comforting thought.
• If appropriate, begin to legitimately think about the decision or action.

If this is a procedure that will work more generally, then these exercises may help:

• Mindfulness meditation. Attention control is critical, mindfulness and a thread on mindfulness
• Noting emotions. Name your emotions, simply and without judgment, as you see them arise.
• Trace emotion causes. When you do manage to notice an emotion and have a moment, practice asking yourself what the proximate cause of that emotion was until it becomes a not-uncommon practice upon noticing a surprising emotion.
• Avoid Optimizing Proxy Measures Train yourself to intuit that optimizing the heuristic measure correlating with your purpose does not optimize your purpose.
• Desire Generalizable Decision Processes Feel uncomfortable with the hint of uncertainty that maybe the algorithm that generated the reason you feel safe would have statistically bad results if applied more generally.
• Check Yourself For BS Practice applying your bullshit detector on your own thoughts.
• Notice Rationalization Directly Actively reward noticing rationalization.