[HOW TO] Learning to top..

[ScVernel]

Hello.
I'm new here and I'm hoping this forum could help.

I am a bottom, in nature. I've always thought and fantasized from the POV of a bottom. My issue is, I would like to "learn" to become versatile. As I'm writing this, I'm imagining getting something like Fleshjack, or a 'holed' toy, may serve my purposes tremendously. But, to continue, I have attempted topping less than a handful of times and have nearly always begun losing my erection within the moments of insertion.
'This' understandable to me as, if I'm not directly stimulating {myself}|being stimulated, I lose erections very quickly. And, not being turned on naturally imagining myself topping, the loss of erection is no surprise. Which lead me to try Viagra on 2 occasions. But in neither situation was there any known effect, to my penis nor my 'drive'.

I'd love to hear from someone who's made the addition, or Switch, from being a total bottom into becoming comfortable being versatile, or even into total Topism (I'm sure that must've happened at least once in history).