Are you sure about the trend still being down? It only partially rebounded, but the $252 low is behind us and once it broke out of the ~$253 wobbling it has been trending upward, not down.
Note: I am *not* saying it cannot go down further. But you said trend and I'm curious as that is not what I'm seeing on $TSLA at all.
Obviously trend depends on the timeframe you are looking to.
Looking at a daily chart, the uptrend that started on april/2018 ended two days ago, when the price stopped making higher-highs.
On a shorter term, we are on a down trend since the peak of august/2018.
To buy, I expect:
0) Selling climax on a strong support, such as today (huge volume, price stopped, record bad news)
1) Upwards intentionality (for example, april 3rd).
2) No supply on the retracement (low volume retracement except probably the typical bear trap in the end)
3) Buy when the retracement is broken
I can search all this on lower timeframes to try to anticipate.
Sorry if I became too technical.