Remove the solder on BR. Slide up or down as needed. Put a heat sink across both. Then reflow solder.

Or cut a heat sink in half and put part of it on both.

LTG : )

Please don't do this, this is NOT a best practice and you will actually be reducing the heatsinks ability shed heat from both your 5V and 18V rectifiers

Please look over the PinWiki page on this.
https://pinwiki.com/wiki/index.php?title=Williams_WPC#Failed_Bridge_Rectifier
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Although I don't agree with cutting the heat sink in half - there is sound reasoning as to why to do this.

When you have one device connected to a heat sink - he controls the thermal expansion and his leads expand proportionally. But there is still some differential between the leads. With only one device, this expansion is slight and you normally don't need to worry about thermal expansion.

With two or more devices connected to the heat sink - one of the devices will always heat up more than the others. This puts stress on all of the devices due to variances in thermal expansion. The proper method to mount more than one device to a heat sink is to thermally relieve the legs of the device -- small kinks in the legs.

For this - I use a "Merry" PC1 lead bender.
https://www.nilemerry.com/PC1-PC-Forming-Pliers-for-bending-lead-wires
Great tool, horrible website and difficult to see what it does. It puts small kinks in leads to allow thermal expansion - about 2mm long. Normally used for TO-220 type transistors but can be used for bridge rectifiers as well.

Hakko also sells lead forming tools but their website is even worse for determining what they do.