How to solve tunnel vision

Give an example
The answer is usually slow down to speed up or improve your process, but often also...it's both.
You play 3 minute games. It's simply not enough time. Play longer times, say 30 minutes. Also practise puzzles daily. Aim to get them right first time in your head before moving a piece. It will help train your brain to calculate and visualise a few moves ahead. The experts on utube and twitch make it look easy but that's because they've been playing for years and learned their craft playing long games.
That is normal if you played less than 500 games. Play a ton of games, it will all start to become more clear after a while. Also: Look at the signs of danger, what are the current dangers on the board? Recognice these dangers. Repetition is key.
Well, if you immediately realize why your move was a bad move, you're actually on the right path. The more you play, the faster your brain will foresee the problems, the fewer your blunders will become. If you already quickly spot your errors, you don't have to become that much faster!
If you're asking about true tunnel vision, what you might need to improve on is looking for alternatives and looking out for the plans of your opponent. You could improve this by first asking yourself - on every move your opponent plays! - what your opponent is threatening with his/her last move. Also look to see if the move opened up lines for other pieces etc. that might carry a threat. After you've done this quick check, you should always, always, always have about 3 candidate moves (in normal positions). Even when it's a recapture, take the time to look for alternatives. In one of my recent games, I saw I could take a piece and be a piece up, but I quickly looked for another move and saw that I could make another move that won the queen because of a mating attack. The old saying holds true: if you see a good move, look for a better one. After you've gotten 3 candidate moves and selected the one you want to play, do a quick tactical blundercheck to see if it doesn't just give away a piece. If this feels like a lot of work for every move, maybe try a slower time control until you've familiarized yourself a bit with this method. In time it'll become second nature and you won't really need to adhere so strictly to this process.

^^^
Looking there...
Slow down and improve your process, then speed up because process becomes easier.

Even the great Bobby Fischer sometimes had "tunnel vision". In one of his games, he calculated out a mate in 4, and later it was pointed out to him that there was a mate in 3 on the board. Fischer in his usual style said, "I had already calculated out the mate in 4, so why would I waste time looking for a faster mate when I had already found the win?" Fischer understood that the objective of the game is not accuracy, but victory.