Hard drive ignores available free space

I have a 500 GB SSD. At one point, it had 2 partitions--one for my regular macOS boot (430 GB), and one for developer previews (~70 GB). At some point, I deleted the developer preview partition, but the freed up space didn't flow back to the main partition. Also, I wasn't able to resize the Macintosh HD partition back to the full 500 GB. How do I get my 70 GB back on the Macintosh HD partition?

Here is the output from diskutil list showing the total drive size and only 429.4 GB available:

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:       Apple_KernelCoreDump                         655.4 MB   disk0s2
   3:                 Apple_APFS Container disk1         429.4 GB   disk0s3

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +429.4 GB   disk1
                                 Physical Store disk0s3
   1:                APFS Volume Macintosh HD            396.5 GB   disk1s1
   2:                APFS Volume Preboot                 43.7 MB    disk1s2
   3:                APFS Volume Recovery                509.8 MB   disk1s3
   4:                APFS Volume VM                      2.1 GB     disk1s4

Solution 1:

The following solution assumes some comfort with the command line - if you aren't comfortable with it, let me know and i will provide a GUI method.

Referring to your picture,

1. click on the line that says "Container disk 1"
2. make a note of the value in the field "physical stores" (let's assume it says disk0s2)
3. In spotlight type 'terminal' and hit return to bring up the command line
4. become an administrator (either su to the administrator or login as one)
5. type the command 'diskutil apfs resizecontainer disk0s2 0' (change disk0s2 to your value).

When the prompt returns, you should have the whole disk back. If not, please make a note of the result and publish it here.