1. SpaceX issued long-term bonds whose coupon (ie, "interest rate") was 6.5%.
2. Those bonds are now trading for less than their face value. That means that if you buy one of those bonds on the secondary market, you will get a return (yield) of 7.387% (if the price of a bond goes down, but the coupon stays the same, the yield goes up).
3. This doesn't affect SpaceX directly, but it tells you that if SpaceX were to issue new bonds today, they would have to offer 7.4% coupon on them, not 6.5%. Note that even though that was caused by a 10% drop in the bond value, it's a 13% increase in cost of borrowing!
SpaceX is a cash-flow negative company that depends on debt and selling equity in order to pay the bills. They will have to issue bonds again, and those bonds will be more expensive.
Note that the shortest maturity bonds don't have to be repaid for 5 years, so the impact on cash is not going to manifest for a while...at least 5 years time (assuming they did another bond offering tomorrow). In that sense it's a nothingburger.
The immediate impact it could have is if spacex depends on issuing new, shorter-term debt (lines of credit, etc) whose price could be impacted by the market's perception of their riskiness.
That's your return if you buy one of those bonds and the bond is paid on schedule. Presumably the market consensus is there's some risk that payment may arrive late or not at all since the yield to maturity has increased since issuance and not as a result of underlying interest rate changes.
For a spread of 300 basis points that's still a very low probability, probably under 5%.
You'll probably get that, but you might not.