Welcome to the site Henry.
I don't think re-learning an instrument will be very different from the first time you learned it. You will have the benefit of having some knowledge but also have the disadvantage of having some old bad habits. Just like learning anything else it is good to:
- set short term goals
- set long term goals
- make a routine
- evaluate and adjust
Without goals you can easily lose focus and forget what you are aiming for. Short term goals are good for letting you know how you are doing and keeps you moving forward. Long term goals gives you a prize to strive for. Make sure your goals are measurable. For example "be good at bass" is not measurable. But play all the songs on album x is.
A routine will help you keep on track. Make sure your routine incorporates the types of activities that will help you reach your goal.
Nothing in life ever goes as plan, so from time to time make sure you step back, check to see how things are going and adjust your goals, and routine accordingly.
I used to play the drums at a high level. I stopped and haven't played in years. I now play multiple stringed instruments, mainly guitar, but if I wanted to pick the drums back up I would do the following:
Make sure my instrument was in good working order. I'd get new heads and sticks (strings and picks) if needed. If it is not in good working order I'd have it repaired if possible or buy a new one. You should do the same with your bass. Get new strings. get a set up at your local shop or buy a new one. Learning on an instrument that is not working properly will not be fun, can be frustrating and maybe even lead to injuries.
I would set a time of day to practice or some how make sure to carve practice time into my day.
List the things that I know I should have worked on when I was younger but didn't. (practice with a metronome. work on ear training. practice rudiments (or scales, arpeggios, etc in your case)). This is your chance to use your experience as a benefit. You are older and hopefully wiser now. Kick those old bad habits now before you re-establish them.
Come up with my practice routine: warmup/exercises, transcribe a new song, work on last week's song, etc... Knowing what you will be doing when you practice will help it go faster and smoother. Nothing is worse for your progress than sitting down and noodling around for an hour. It doesn't help you improve much and sucks up all your time.
I'd play along to music I like.
I'd record myself playing. Nothing will bring all the flaws to your attention like a video or audio recording of your playing.
Play with others.
I hope this helps. A good teacher can help you with all this stuff, and is worthwhile but not 100% necessary as you have the benefit from already knowing a lot of stuff that a typical beginner does not. The most important things are have fun, and play, play, play.