Vostro 3470, removed bootable USB stick, no boot

You cannot install windows 7 on a windows 10 computer. Windows 7 cannot run the hardware that didn't exist years ago. Reinstall Windows 10. You will have to do a clean custom install.

Windows 7 has only about 5 months left of MS support so you need to upgrade any other computer that still has it.

https://answers.microsoft.com/en-us/windows/forum/all/windows-7-support-will-end-on-january-14-2020/103f68c5-c977-42b6-9f9f-3d1ea4c652d9

Legacy booting and windows 7 are NOT an option for 2018 Vostro 3470 Mini Tower 8th Generation Desktop Computer PC Intel Quad Core i3-8100

Intel's seventh generation Core processors, and newer are Windows 10 only operating system support.  Nobody can help you and you will not be able to run WINDOWS 7 32 bit on this machine EVER.

Skylake (Intel 6th Generation Core processors) will support Windows 7, 8.1,10. What is Skylake and what do I need to know about it? A: Skylake refers to the 6th Generation of the Intel Core processor design and it is the successor to the 5th generation Broadwell chipset. Some important issues with the Skylake chipset include: No longer includes support for the USB 2.0 bus (Windows 7 requires USB 2.0 support unless specific USB 3.1 drivers are incorporated into your Windows 7 image.)
Thunderbolt 3.0 high speed data transport support. The 6th Generation Intel Core i7-6500 for example supports windows 7.
Iris Pro Graphics capable of 4k display on up to 3 screens.

WIN7 and earlier are never supported and this is enforced by INTEL, Microsoft, NVIDIA, ATI, QUALLCOMM etc.

Furthermore newer GPUs will be 64 BIT only from now on period end.

You will have to look for Optiplex 9020 5040 7040 model.

https://www.dell.com/support/article/us/en/04/sln312414/dell-command-deploy-driver-packs-for-enterprise-client-os-deployment

Optiplex Systems - CAB Availability (follow the links for CAB details and to download)